Droplet-on-demand ink jet printing systems eject ink droplets from print head nozzles in response to pressure pulses generated within the print head by either piezoelectric devices or thermal transducers, such as resistors. The ejected ink droplets, commonly referred to as pixels, are propelled to specific locations on an image receiving member where each ink droplet forms a spot on the member. The print heads have droplet ejecting nozzles and a plurality of ink containing channels, usually one channel for each nozzle, which interconnect an ink reservoir in the print head with the nozzles.
In a typical piezoelectric ink jet printing system, the pressure pulses that eject liquid ink droplets are produced by applying an electric pulse to the piezoelectric devices, one of which is typically located within each one of the inkjet channels. Each piezoelectric device is individually addressable to enable a firing signal to be generated and delivered for each piezoelectric device. The firing signal causes the piezoelectric device receiving the signal to bend or deform and pressurize a volume of liquid ink adjacent the piezoelectric device. As a voltage pulse is applied to a selected piezoelectric device, a quantity of ink is displaced from the ink channel and a droplet of ink is mechanically ejected from the nozzle, commonly called an inkjet or jet, associated with each piezoelectric device. The ejected droplets form an image on the image receiving member opposite the print head. The respective channels from which the ink droplets were ejected are refilled by capillary action from an ink supply.
In some phase change or solid ink printers, the image receiving member is a rotating drum or belt coated with a release agent and the ink medium is melted ink that is normally solid at room temperature. The print head ejects droplets of melted ink onto the rotating image receiving member to form an image, which is then transferred to a recording medium, such as paper. The image receiving member is prepared for receipt of the ejected ink by the application of release agent to an imaging area on the image receiving member by a drum maintenance unit or other release agent applicator. The layer of release agent on the image receiving member forms a surface on which the ink image is formed and facilitates the transfer of the ink image from the receiving member to a recording medium. The transfer is generally conducted in a nip formed by the rotating image member and a rotating pressure roller, which is also called a transfix roller. The pressure roller may be heated or the recording medium may be pre-heated prior to entry in the transfixing nip. As a sheet of paper is transported through the nip, the fully formed image is transferred from the image receiving member to the sheet of paper and concurrently fixed thereon. This technique of using heat and pressure at a nip to transfer and fix an image to a recording medium passing through the nip is typically known as “transfixing,” a well known term in the art, particularly with solid ink technology.
The time required for image generation and transfer is essentially fixed in a printer by frequency at which the inkjet ejectors can be operated and the overhead operations required to prepare the image receiving member and to transfer the image from the image receiving member to recording media. In previously known printing systems, the application of the release agent to the image receiving member occurs over the full expected imaging region of the member. Likewise, the transfix operation has always been performed by engaging the image receiving member with the transfix roller near the media leading edge and withdrawing the roller at or near the trailing edge of the media. The release agent application and transfix cycles operate at a slower drum speed than imaging or media exit so the total time for image generation and transfer is affected. Printing in a manner that improves throughput without degrading image receiving member preparation or the efficiency of image transfer to recording media would be useful.